In the operation of screw machines of known design, the bar stock has been fed into the machine in long lengths and this stock has had a very considerable tendency to vibrate transverse to its length. Usually the rotating bar stock was passed through an elongated guide tube held stationary at the inlet side of the screw machine. The rotating bar stock has a loose fit inside the non-rotating guide tube and it is free to vibrate transversely, striking the tube and thereby causing appreciable noise and often damaging the stock itself, particularly if it is of hexagonal or other polygonal, sharp cornered cross-section. Excessive noise in a machine shop is an occupational hazard which can be damaging to the safety, health and well-being of workers there, and it is contrary to federal policy, as expressed in the Occupational Safety and Health Act.
Various proposals for solving the noise problem, as disclosed in U.S. Pat. Nos. 1,506,107 and 1,506,108, 3,828,630 and 1,935,999, have included the use of mineral wool packing or the like inside the guide tube, rotatable bushings of leather, fiber, polyurethane or other suitable material inside the guide tube, and a metal coil inside the guide tube. Also, U.S. Pat. No. 3,785,468 provides circumferentially spaced metal rollers, mounted on right-angled metal brackets, for guiding bar stock inside a guide tube.